1. Field of the Invention
The present invention relates to a transmission terminal station apparatus for transmitting data received from a low-order group terminal device to a high-order group terminal station device, a transmission terminal station apparatus for transmitting data received from a high-order group terminal station device to a low-order group terminal device, and a network system including these transmission terminal station apparatuses.
2. Prior Art
With an advance in information systems in recent years, line capacities in a communication network increase. In the field of optical communications, optical fibers which are physical resources of optical lines tend to be short. In contrast to this, the shortage of optical fiber are compensated for by replacing a plurality of low-speed lines into high-speed lines by using a high-order group terminal-station device (called xe2x80x9coverlayxe2x80x9d).
FIGS. 5A and 5B are diagrams for explaining the overlay of an optical communication network. As shown in FIG. 5, the following optical communication network is assumed. That is, the optical communication network is constituted by a plurality of low-order group terminal devices (indicated by blocks in FIG. 5A), and the low-order group terminal devices are connected to each other through low-speed lines (OC-12 or OC-48).
A site A in FIG. 5A has low-order group terminal devices T1 to T3, and a site B has low-order group terminal devices T4 to T6. The low-order group terminal devices T1 to T3 are connected to the low-order group terminal devices T4 to T6 through low-speed lines (e.g., OC-48) L1 to L3. The low-order group terminal device T1 and the low-order group terminal device T4 are transparent to each other, the low-order group terminal device T2 and the low-order group terminal device T5 are transparent to each other, and the low-order group terminal device T3 and the low-order group terminal device T6 are transparent to each other. Note that OC-12 and OC-48 represent optical carrier levels (optical speed standards) defined by SONET (Synchronous Optical Network) serving as one of SDHs (Synchronous Digital Hierarchies).
In this case, as shown in FIG. 5B, high-order group terminal station devices K1 and K2 are arranged in the sites A and B. Each of the high-order group terminal station devices K1 and K2 accommodates a low-order group terminal device in the site to which the corresponding high-order group terminal station device belongs. The high-order group terminal station device K1 and the high-order group terminal station device K2 are connected to each other through a high-speed line (e.g., OC-192) L4.
Each of the high-order group terminal station devices K1 and K2 makes OC-48xc3x974 lines multiplexed to OC-192 transparent in accordance with the transparent relationships of the low-order group terminal devices T1 to T6. In this manner, the low-speed lines L1 to L3 of OC-48 are replaced with the high-speed line L4 of OC-192 to compensate for the shortage of optical fiber.
At this time, the high-order group terminal station devices K1 and K2 are pseudo intermediate repeater device with reference to the low-order group terminal devices T1 to T6. That is, the low-order group terminal devices T1 to T6 are arranged such that the low-order group terminal devices T1 to T6 can transmit data to the low-order group terminal devices which are transparent to each other in FIG. 5A without regarding the presence of the high-order group terminal station devices K1 and K2 (low-order group terminal devices T1 to T6 can perform transparent transmission).
According to the optical communication network shown in FIG. 5B, for example, when data is transmitted from the low-order group terminal device T1 of the site A to the low-order group terminal device T4 of the site B, the low-order group terminal device T1 transmits data to the high-order group terminal station device K1.
At this time, the low-order group terminal device T1 regards only that the data is transmitted to the low-order group terminal device T4. the high-order group terminal station device K1 multiplexes data received from the low-order group terminal devices T1 to T3 to transmit the multiplexed data to the high-order group terminal station device K2.
The high-order group terminal station device K2 separates the data received from the high-order group terminal station device K1, and transmits, of the separated data, data to be transmitted to the low-order group terminal device T4 to the low-order group terminal device T4. In this manner, the low-order group terminal device T4 receives the data transmitted from the low-order group terminal device T1. The low-order group terminal device T4 regards only that the data is received from the low-order group terminal device T1.
Even if a high-order group terminal station device is inserted between low-order group terminal devices by overlay as described above, it is demanded that the same transmission/reception as that performed when low-order group terminal devices are directly connected through a low-speed line is should be performed between transparent low-order group terminal devices (e.g., the low-order group terminal device T1 and the low-order group terminal device T4, the low-order group terminal device T2 and the low-order group terminal device T5, and the low-order group terminal device T3 and the low-order group terminal device T6 which are shown in FIG. 5A).
With respect to the above demand, in a conventional optical communication network, the following problems are posed. FIG. 6 is a diagram showing problems in a conventional optical communication network. FIG. 6 shows the low-order group terminal devices T1 and T4 and the high-order group terminal station devices K1 and K2 which are shown in FIG. 5B. In the optical communication network, when data is transmitted between transmission terminal station apparatuses (between low-order group terminal devices or between a low-order group terminal device and a high-order group terminal station device), the data is transmitted while the data is stored in a SONET frame (SDH frame).
The SONET frame (SDH frame) has a payload for storing user data (transmission information) and an overhead in which operation maintenance information of a network is stored. The overhead is constituted by a section overhead (SOH), a line overhead (LOH), or the like.
When the low-order group terminal device or the high-order group terminal station device receives a SONET frame, the corresponding group terminal station terminates the SONET frame, generates a new SONET frame depending on an output port of data stored in the SONET frame, and stores data to be transmitted to the payload of each SONET frame to transmit the data to the corresponding output port. In this process, the contents of the overhead of the new SONET frame are new contents to be inserted by the low-order group terminal device or the high-order group terminal station device.
A byte (called a B2 byte) used for monitoring a code error between transmission terminal station apparatuses is stored in the LOH of the overhead. The B2 byte is inserted into the LOH of a SONET frame in a transmission terminal station apparatus on the transmission side, detected by a transmission terminal station apparatus (transmission terminal station apparatus on the reception side) which terminates the SONET frame, and used for monitoring a code error (calculating the number of parity errors).
A monitor result (the number of parity errors) obtained by monitoring a code error is transmitted to the transmission terminal station apparatus on the transmission side (L-FEBE). The transmission terminal station apparatus on the transmission side switches a line used in data transmission to another line when the number of parity errors exceeds a threshold value. In this manner, the transmission quality of data can be maintained.
In FIG. 6, data is transmitted from the low-order group terminal device T1 to the low-order group terminal device T4, a SONET frame in which the data is stored is transmitted from the low-order group terminal device T1 to the high-order group terminal station device K1. At this time, a predetermined B2 byte is inserted into the LOH of the SONET frame.
When the high-order group terminal station device K1 receives the SONET frame from the low-order group terminal device T1, the high-order group terminal station device K1 terminates the SONET frame, and the high-order group terminal station device K1 detects the B2 byte from the terminated SONET frame. The high-order group terminal station device K1 calculates the number of parity errors by using the detected B2 byte, and notifies the low-order group terminal device T1 of the result. On the other hand, the high-order group terminal station device K1 generates a new SONET frame in which the data received from the low-order group terminal device T1, inserts a new B2 byte into the LOH of the new SONET frame. Thereafter, the high-order group terminal station device K1 transmits the SONET frame to the high-order group terminal station device K2.
Thereafter, when the high-order group terminal station device K2 receives the SONET frame from the high-order group terminal station device K1, the high-order group terminal station device K2 performs the same operation as that performed in the high-order group terminal station device K1, and the B2 byte newly inserted in the high-order group terminal station device K2 is received by the low-order group terminal device T4.
At this time, since the low-order group terminal device T4 does not regard the presence of the high-order group terminal station devices K1 and K2, the low-order group terminal device T4 handles the B2 byte (B2 byte inserted by the high-order group terminal station device K2) included in the received SONET frame, and the number of parity errors transmitted from the low-order group terminal device T4 to the low-order group terminal device T1 is received by the high-order group terminal station device K2.
Therefore, the high-order group terminal station device K2 does not switch lines when the number of parity errors received from the low-order group terminal device T4 is within an allowable range. For this reason, although the number of parity errors of the B2 byte between the low-order group terminal device T1 and the low-order group terminal device T4 is out of the allowable range, when the number of parity errors of the B2 byte between the high-order group terminal station device K2 and the low-order group terminal device T4 is within the allowable range, the high-order group terminal station device K2 does not switch lines. In this manner, data may not be properly transmitted between the low-order group terminal device T1 and the low-order group terminal device T4.
As described above, when the high-order group terminal station device is inserted between the low-order group terminal devices (overlay is performed), a B2 byte cannot be transmitted in a transparent mode between the low-order group terminal devices, and a code error cannot be properly monitored by the low-order group terminal device on the reception side. As a result, switching of lines may not be properly performed.
More specifically, when overlay is performed, by inserting a high-order group terminal station device, operation maintenance information stored in an overhead of a frame transmitted from a low-order group terminal device on the transmission side is not received by a low-order group terminal device on the reception side. Therefore, there is a problem that operation maintenance of a network using the operation maintenance information is not performed.
The present invention has been made in consideration of the above problem, and has as its object to provide a transmission terminal station apparatus and a network system in which information related to operation maintenance information stored in a frame received from a low-order group terminal device can be transmitted to a high-order group terminal station device, and a network system.
For example, it is an object of the present invention to provide a transmission terminal station apparatus and a network system in which a low-order group terminal device on a reception side can monitor a code error between the low-order group terminal device on the reception side and a low-order group terminal device on a transmission side even if a high-order group terminal station device is inserted between low-order group terminal devices.
The first aspect of the present invention is a transmission terminal station apparatus in which a low-order group terminal device is connected through a low-speed line and a high-order group terminal station device is connected through a low-speed line. The transmission terminal station apparatus includes: (1) a detection unit which, when a frame including a payload in which data to be transmitted is stored and an overhead in which operation maintenance information of a network is stored is received from the low-order group terminal device, detects, as detection information, information related to the operation maintenance information to be transmitted from the overhead of the frame to the high-order group terminal station device; (2) a first insertion unit for inserting the detection information detected by the detection unit into a space area of the frame; (3) a multiplexing unit for generating a multi-frame including the frame; (4) and a second insertion unit for inserting new operation maintenance information into an overhead of the multi-frame generated by the multiplexing unit to transmit the operation maintenance information toward the high-order group terminal station device.
According to the first aspect, information related to operation maintenance information which is not transmitted to a high-order group terminal station device in the prior art can be transmitted can be transmitted to a high-order group terminal station device.
The first aspect can also be applied to not only an optical communication network, but also a network which transmits data by using only an electric signal. The frames include not only an SDH frame and a SONET frame, but also, a packet, a frame relay frame, an ATM cell, and the like. The information related to the operation maintenance information and serving as detection information includes operation maintenance information itself and information obtained by processing the operation maintenance information.
The second aspect of the present invention is a transmission terminal station apparatus in which a low-order group terminal device is connected through a low-speed line, and a high-order group terminal station device is connected through a high-speed line. The transmission terminal station apparatus includes: (1) a first extraction unit which, when a multi-frame obtained by multiplexing a plurality of frames each having a payload in which data to be transmitted is stored and an overhead in which operation maintenance information of a network is stored is received from the high-order group terminal station device, extracts the operation maintenance information stored in the overhead of the multi-frame; (2) a second extraction unit for extracting detection information serving as information related to the operation maintenance information stored in the overhead of each frame when each frame included in the multi-frame is received by the high-order group terminal station device from each frame included in the multi-frame; (3) a separation unit for separating the multi-frame into a plurality of frames; and (4) a setting unit for inserting new operation maintenance information generated by using information related to the operation maintenance information extracted by the first extraction unit and the detection information extracted by the second extraction unit into the overhead of each frame separated by the separation unit to transmit the operation maintenance information to the low-order group terminal device.
The first aspect may further include: a first extraction unit which, when a multi-frame obtained by multiplexing a plurality of frames is received from the high-order group terminal station device, extracts operation maintenance information stored in an overhead of the multi-frame; a second extraction unit for extracting detection information from each frame included in the multi-frame; a separation unit for separating the multi-frame into a plurality of frames; and a setting unit for inserting new operation maintenance information generated by using information related to the operation maintenance information extracted by the first extraction unit and the detection information extracted by the second extraction unit into the overhead of each frame separated by the separation unit to transmit the operation maintenance information to the low-order group terminal device.
In this manner, the operation maintenance information and the detection information of the multi-frame received from the high-order group terminal station device are reflected on the contents of the operation maintenance information transmitted to the low-order group terminal device, and the low-order group terminal device can perform operation maintenance of a network between a low-order group terminal device in which operation maintenance information corresponding to the detection information and the low-order group terminal device.
In the first aspect, the operation maintenance information is code error monitoring information, and the detection unit may detect information related to the code error monitoring information stored in the overhead of a frame received from the low-order group terminal device as the detection information.
In the first aspect, the frame is an SDH frame or a SONET frame, the operation maintenance information is a B2 byte, and the detection unit may detect, as the detection information, the number of errors calculated by using the B2 byte stored in the overhead of the frame received from the low-order group terminal device.
As a matter of course, the operation maintenance information and the detection information in the present invention include, e.g., in addition to code error monitoring information (B2 byte), other operation maintenance information (other bytes) defined with reference to an SDH or SONET frame.
In the second aspect, the operation maintenance information is code error monitoring information, the detection information is information related to code error monitoring information stored in the overhead of each frame when the high-order group terminal station device receives each frame included in the multi-frame, and the setting unit may insert new code error monitoring information generated by using information related to the code error monitoring information extracted by the first extraction unit and the detection information extracted by the second extraction unit into the overhead of each frame separated by the separation unit.
In the second aspect, the frame is an SDH frame or a SONET frame, the operation maintenance information is a B2 byte, and the setting unit may insert a B2 byte having a value obtained by reflecting the number of errors of a B2 byte extracted by the first extraction unit and the number of errors of a B2 byte extracted as detection information by the second extraction unit on an initial value of a B2 byte to be inserted into the overhead of each of the frames separated by the separation unit into the overhead of the corresponding frame as new B2 byte.
In the first aspect, the first insertion unit may insert the detection information into a space area of the overhead of the frame.
The third aspect of the present invention is a network system including a first high-order group terminal station device to which a first low-order group terminal device is connected through a low-speed line, and a second high-order group terminal station device to which the first high-order group terminal station device is connected through a high-speed line and to which a second low-order group terminal device is connected through a low-speed line. The first high-order group terminal station device has: a detection unit which, when a frame including a payload in which data to be transmitted is stored and an overhead in which operation maintenance information of a network is stored is received from the first low-order group terminal device, detects, as detection information, information related to the operation maintenance information to be transmitted from the overhead of the frame to the second high-order group terminal station device; a first insertion unit for inserting the detection information detected by the detection unit into a space area of the frame; a multiplexing unit for generating a multi-frame including the frame; and a second insertion unit for inserting new operation maintenance information into an overhead of the multi-frame generated by the multiplexing unit to transmit the operation maintenance information toward the second high-order group terminal station device. The second high-order group terminal station device has: a first extraction unit which, when the multi-frame is received from the first high-order group terminal station device, extracts the operation maintenance information stored in the overhead of the multi-frame; a second extraction unit for extracting the detection information from each frame included in the multi-frame; a separation unit for separating the frames included in the multi-frame; and a setting unit for inserting new operation maintenance information generated by using information related to the operation maintenance information extracted by the first extraction unit and the detection information extracted by the second extraction unit into the overhead of each frame separated by the separation unit to transmit the operation maintenance information to the second low-order group terminal device the separation unit.
According to the transmission terminal station apparatus and the network system of the present invention, information related to operation maintenance information stored in a frame received from a low-order group terminal device can be transmitted to a high-order group terminal station device.
In addition, according to the transmission terminal station apparatus and the network system of the present invention, even if a high-order group terminal station device is inserted between low-order group terminal devices, code error monitoring information inserted by a low-order group terminal device on a transmission side can be received by a low-order group terminal device on a reception side. For this reason, the low-order group terminal device on the reception side can monitor a code error between the low-order group terminal device on the reception side and the low-order group terminal device on the transmission side.